A complicated calculus-based anti-spam CAPTCHA

Eggheads at the Ruđer Bošković Institute in Zagreb, Croatia, are having some geeky fun with their web forms.

If you want to login to the institute's Quantum Random Bit Generator service, you will be asked the usual questions like your username and password, but then you'll be faced by a mathematical problem that may give you a nighmarish memories of your schooldays doing advanced calculus.

Hmm.. it's a bit more complicated than the typical sort of CAPTCHA used by websites around the world to try to block spam bots and automated systems:

Sometimes, of course, these randomly-generated CAPTCHAs can go very wrong - potentially causing unintended offense to some amusement.

Somehow I don't think the calculus-based CAPTCHA is going to catch on with the general public.

29 Responses to A complicated calculus-based anti-spam CAPTCHA

I'm sure I've seen similar CAPTCHAs ages ago. (Though never "in the wild".) More complicated ones too. This one isn't too difficult. And having people solve a CAPTCHA like this before allowing them to leave comments on your website, may keep the vast majority of daft comments at bay!

As far as I can see, the differentiation always gives (1 or 0)*prefaktor [see sin/cos(pi/2)]. Thus by reading just a part of the equation, without any other operation than MUL, the solution can be found.

I don't think this site is intended for the average child. Those gifted children who might be visiting the site for a legitimate purpose would likely be able to solve the calculus questions. Those who can't solve the question probably are not the intended users of the site.

Some of the captcha questions on this particular site are actually no harder than the skill testing questions one might find on a bag of chips. For example, this is what I got on just one reload of the page: -1 + (-2) + 3 - (-1) - 0 + (-3) + 3 = ?

Obviously, it doesn't make sense for the average person who may never take a calculus class, but for those of us who wish to keep our skills sharp, it would be great to be able to select this type of captcha. I used to do math tournaments, but I haven't had a math class (apart from stats) in over ten years and I'm terribly rusty.

Even a simple browser add-on that gated every 10th or 20th page with a math problem would be awesome. Someone please get on this. :)

I had to reload the page twice before I could solve it. Personally, I like the mathematical Captchas and far from sieving the desirable commenters, it would just have someone use their mind before they post (something many people do not).

About the author

Graham Cluley runs his own award-winning computer security blog at https://grahamcluley.com, and is a veteran of the anti-virus industry having worked for a number of security companies since the early 1990s. Now an independent security analyst, he regularly makes media appearances and gives computer security presentations. Follow him on Twitter at @gcluley